Electrostatic deposition apparatus

ABSTRACT

Apparatus for providing the charged particles includes an electrically insulative belt having a surface upon which the organoplastic material is placed and transported to an electrical charging and atomizing zone. Positioned within the charging and atomizing zone is means having an extended or elongated edge at high electrical potential. The extended edge is so positioned as to be substantially transverse of and in close proximity with the surface of the insulative means transporting the organoplastic material. A high intensity electric field extends from the extended edge to, or in some instances, through the substrate if the substrate is porous and fabricated from an insulative rather than a conductive material. The position of the extended edge at high electrical potential relative to the organoplastic material causes the organoplastic material to be formed into charged particles that are projected toward and deposited upon the substrate.

Umted States Patent 1 [111 3,776,187 Probst Dec. 4, 1973 [54]ELECTROSTATICDEPOSITION 3,221,992 12/1965 Sedlacsik, Jr. et a1 239/15 7APPARATUS 3,512,502 5/1970 Drum 118/626 X [75] lnvento r: Richard O.Probst, Indianapolis, Primary Examiner Morris Kaplan Attorney-Merrill N.Johnson et al. [73] Assignee: Ransburg Electro-Coating Corp.,

Indianapolis, Ind.

[22] Filed: May 3, 1972 [21] Appl. No.: 249,867

Related US. Application Data [62] Division of Ser. No. 061,308, Aug. 5,1970, Pat. No.

[52] US. Cl. 118/626, 317/3 [51] Int. Cl 1305b 5/02 [58] Field of Search118/626, 637; 117/17, 17.5; 346/1 NQ; 317/3; 239/3, 15

[56] References Cited UNITED STATES PATENTS 2,651,287 9/1953 Turner118/637 UX 2,695,002 11/1954 Miller 239/15 X 2,723,646 1l/1955Ransburg.... 118/626 2,893,893 7/1959 Crouse 118/626 X 3,010,428 l1/l961Sedlacsik 118/626 X [57] ABSTRACT Apparatus for providing the chargedparticles includes an electrically insulative belt having a surface uponwhich the organoplastic material is placed and transported to anelectrical charging and atomizing zone. Positioned within the chargingand atomizing zone is means having an extended or elongated edge at highelectrical potential. The extended edge is so positioned as to besubstantially transverse of and in close proximity with the surface ofthe insulative means transporting the organoplastic material. A highintensity electric field extends from the extended edge to, or in someinstances, through the substrate if the substrate is porous andfabricated from an insulative rather than a conductive material. Theposition of the extended edge at high electrical potential relative tothe organoplastic material causes the organoplastic material to beformed into charged particles that are projected toward and depositedupon the substrate.

3 Claims, 2 Drawing Figures ELECTROSTATIC DEPOSITION APPARATUS This is acontinuation, division, of application Ser. No. 061,308, filed Aug. 5,1970 and now U.S. Pat. No. 3,676,194.

The present invention relates to electrostatic spraying of anorganoplastic material and, more particularly, to an improvedelectrostatic apparatus in which a polymeric organoplastic foam materialis atomized and electrostatically deposited upon a substrate.

The use of a thin sheet or layer of a polymeric organoplastic foammaterial as backing for a woven or non-woven fiber webs such ascarpeting has increased during the last several years due to, amongother things, the production costs associated with non-foamed materials.A number of polymeric organoplastic foam materials for use as carpetbacking have been proposed. Such polymeric organoplastic foam materialsinclude flexible foams such as polyolefin, polyethylene, polyurethaneand the like. The above flexible polymeric organoplastic foam materialsall have some advantages when used as backing for carpeting. Forexample, flexible polyethylene foam does not impart an objectionableodor to the carpet and, usually, an adhesive is not required to adherethe flexible polyethylene foamto the carpet. Nevertheless, flexiblepolyurethane foam is becoming increasingly more popular as a backingmaterial for carpeting because of its relatively inert chemical nature,elasticity, drapability dimensional stability,

thermal insulation, wear resistance, shock absorption and low cost.

An automated apparatus for dispensing a flexible polyurethane foammaterial uses a reciprocating mixing head to deposit foamablepolyurethane liquid in a moving mold cavity having the desiredconfiguration. Most mixing heads use a chamber which receives theseveral components which comprise the polyurethane. Located within thechamber is an agitator or stirrer which is immersed in the componentsand which revolves for the purpose of mixing the components. The mixedcomponents of the polyurethane exit the mixing head as a liquid streamwhich is deposited in the mold before foaming thereof takes place. It isnecessary to revolve the agitator at high speed in order to effectivelymix the components into a homogeneous mixture within the time allowedfor mixing. The mixture while in the mold reacts to generate a thickslab of foam.

Depositing a polyurethane plastic foam using the above automatedapparatus including a mixing head using an agitator or stirrer issatisfactory for many applications; however, certain processingrestrictions are imposed. For example, after the polyurethane foams inthe mold cavity and is suitably cured and aged, it is removed from themold cavity as thick slabs and sliced into relatively thin sheets on theorder of one-eighth to one-fourth inch for subsequent bonding to thecarpeting as backing material. The polyurethane tends, however, to foamirregularly thereby providing a thick slab having a rather irregularexterior surface. As a result of this irregular surface contour, up toabout 15 per cent by volume of the foamed polyurethane may be virtuallyuseless as backing material for carpeting.

The usable slices of polyurethane foam are then bonded to the carpetingby an adhesive which. is compatible with both the fibers of thecarpeting and the polyurethane foam.

It should be seen that a substantial cost is associated with the stepsof cutting, fitting, and bonding the polyurethane foam to the fibers ofthe carpeting.

Electrostatic spraying of coating materials onto a substrate has severaladvantages. These advantages include providing an adherent, relativelythin, substantially uniform layer of coating material over the surfaceof the substrate without the use of cements, excess material removers,materials levelers and the like.

It is, therefore, an object of the present invention to provide anelectrostatic apparatus for dispensing an organoplastic material that isadapted to provide a relatively thin, but substantially uniformly thick,adherent layer of the organoplastic material upon a substrate. Anotherobject of the present invention is to provide an apparatus forelectrostatically atomizing a foamable polymeric organoplastic material;the apparatus including an extended edge at high potential in contactwith at least some of the foamable polymeric organoplastic to be chargedand atomized.

Generally speaking, the present invention relates to an electrostaticapparatus for electrostatically deposit inganorganoplastic material suchas a foamable polymeric organoplastic material upon a substrate such asa woven or non-woven bundle of fibers. The apparatus includes anextended edge at high potential which provides a high intensity electricfield so as to electrostatically atomize the organoplastic materialcarried by an insulative belt.

his to be understood that the present invention is applicable toorganoplastic materials other than flexible polyurethane foam. Examplesof other organoplastic materials are polymeric organoplastic foamsincluding but not limited to foamable thermoplastic polymers, foamableurea-formaldehyde, foamable phenolics, foamable epoxy resins, foamablesilicones and the like. The foams may be either flexible or rigid. Ofcourse, flexible foam materials are preferred over rigid foam materialsif the foam material is to be used as backing for a carpet. The conceptsof the present invention are also applicable to the deposition oforganoplastic materials onto a myriad of electrically insulative andconductive substrate materials including but not limited to fibrouswebs, wood, plastic, ceramic, metal and the like.

The purpose of illustration and not for the purpose of limitation, theoperation of the apparatus and method embodying the concepts of thepresent invention shall be described in conjunction with a flexiblepolyurethane foam and woven fiber bundle.

In the drawing:

FIG. 1 is a diagrammatic illustration embodying the concepts of thepresent invention; and

FIG. 2 is a perspective view of the apparatus illustrated in FIG. 1.

Referring now to the several FIGURES of the drawing and in particular toFIG. 1, an apparatus 10 for atomizing and applying electrically chargedparticles 11 of a foamable polyurethane liquid to a displaceable wovenfiber bundle 12 is shown.

The apparatus 10 includes a displaceable, endless belt 13 fabricatedfrom a resilient, electrically insulative material such aspolytetrafluorethylene. The belt 13 is displaced in the direction ofarrow 14 by any suitable means such as by cylinders 15 and 16. Thecylinders l5 and 16 may be driven in the clockwise direction by anysuitable drive means (not shown) such as a motor connected to each ofthe cylinders through any suitable speed reduction gear system (notshown).

A reaction or mixing head 32 includes a mixing chamber (not shown)employing a suitable revolving agitator (not shown) immersed in thecomponents which will constitute the polyurethane. The component mayenter the mixing chamber of the mixing head 32 through individual slotsprovided therein. For example, the polyester, the polyisocyanate, andsuitable activator solution may be separately pumped to the mixing head32 or a mixture of polyester and polyisocyanate may be pumped to themixing head where it is mixed with the activator solution. The foamableliquid emerges from the mixing head 32 through aperture 18 of conduit17. The aperture 18 of conduit 17 is adjacent surface 28 of belt 13. Themixing head 32 and the conduit 17 are reciprocated across the width ofthe belt 13 by any suitable means to insure a relatively uniform depositof the mixture of the foamable polyurethane liquid on surface 28 of belt13 in the nip between the belt and blade 20. Parallel spaced guides 30and 31 serve to predeterminately locate mixing head 32 with respect tothe endless belt 13 and blade 20 as the mixing head and the conduitreciprocate across the belt. It is preferred that the components of thepolyurethane be mixed immediately prior to contact with the surface 28of the endless belt 13 in order to minimize premature foaming of thepolyurethane liquid. Foaming of the polyurethane liquid may becontrolled by the addition thereto of suitable additives. Endless belt13 transports the newly mixed, but as yet unfoamed polyurethane liquidin the direction of arrow 14.

Adjacent to but spaced from the endless belt 13 is blade 20. Blade 20serves to limit the thickness of the polyurethane liquid as it passesthereunder so that polyurethane liquid is distributed substantiallyuniformly over the surface of the endless belt 13 as the belt moves inthe direction of arrow 14. It is seen that blade 20 assists in providingdetermined amounts of polyurethane liquid to charging and atomizing zone21 of the apparatus 10.

The charging and atomizing zone 21 provides electrostatic charging andatomization of the polyurethane liquid provided by the mixing head 32.Included within the charging and atomizing zone 21 is wedge-shaped means26 having elongated tip 22 which extends thwartwise the endless belt 13.The elongated tip 22 of the wedge-shaped means 26 is adapted to form theendless belt 13 into a relatively attenuated edge as shown at 23. Forbest results, the attenuated edge 23 should be appropriately spaced fromand substantially perpendicular to the fibrous web 12 as shown in theseveral Figures of the drawing.

Disposed adjacent the surface of the endless belt 13 and in the chargingand atomizing zone 21 is extended edge 25. Preferably, the extended edge25 is relatively sharp and fabricated from any suitable wear resistant,electrically conductive material such as cold-rolled steel and the like.It is preferred that the extended edge 25 be so situated with respect tothe polyurethane liquid that it engages with such liquid at aboutattenuated edge 23 of endless belt 13.

The extended edge 25 is connected to one terminal of high voltage powersupply 27 which is capable of providing up to 130,000 volts directcurrent to edge 25. The other terminal of power supply 27 is grounded.The extended edge 25 traverses the width of the endless belt 13 so as toprovide an electrostatic field of high intensity between itself and theweb material. The high density field causes charging and atomizationofpolyurethane liquid from attenuated edge 23 of endless belt 13. t

It was found that substituting the extended edge 25 for wedge-shapedmeans 26 and connecting the edge to a high potential did not provide anelectrostatic field of sufficient intensity at the voltages hereinsuggested to achieve the desired electrostatic deposition. v

The extended edge 25 may be spaced 6 to 10 inches or more from thesurface of the fibrous web material 12 to be coated by polyurethanefoam. The extended edge 25 and the attenuated edge 23 are each spacedabout the same distance from the web material 12. It is preferred that avoltage gradient of about 3,000 to 10,000 volts'per inch, and preferablyin the neighborhood of 8,000 to 9,000 volts per inch, be providedbetween the extended edge 25 and the vicinity of fibrous web 12. It isto be understood that the voltage gradient necessary to provide anelectrostatic field of an intensity necessary to achieve the desiredresults may vary depending on, among other things, the organoplasticmaterial to be charged and atomized.

To effect atomization of the polyurethane liquid and electrostaticdeposition thereof on the fibrous web 12 as it passes beneath apparatus10, an electrostatic field of high intensity strength should bemaintained between the extended edge 25 and the web 12. It isrecognized-that where the substrate to be coated is of an electricallynon-conductive material such as wood, it

should be rendered electrically conductive by a suitable means such asby treatment with a conductive solution of the type described in US.Letters Pat. No. 3,236,679 and earthed or grounded; or in the case of anon-conductive but relatively porous web 12, it may be earthed orgrounded by placing thereunder a grounded or earthed electricallyconductive support such as support plate 29. The charged particles ofthe polyurethane liquid are attracted to and deposited upon the fibrousweb 12 as a relatively thin layer.

The polyurethane may include a suitable additive which controls foamingof the urethane until after it has i been electrostatically charged,atomized and deposited upon the substrate. It is desirable that foamingof the polyurethane take place just after deposition upon the web 12.

The following example is illustrative of electrostatically depositingparticles of a foamable polyurethane onto a woven carpet.

EXAMPLE A carpet 12 of woven fabric about 6 feet wide is effectivelygrounded in the atomizing zone by a grounded or earthed conductivesupport plate 29 underlying the carpet and over which the carpet isprocessed while in the atomizing zone 21. The surface of the carpet tobe coated with particles 11 of a foamable, flexible polyurethane whilein the atomizing zone is spaced about 10 inches from the extended edge25 at high electrical potential. The extended edge 25, connected to highvoltage direct current power source 27, possesses a length approximatelyequal to the width of the carpeting 12. A high intensity electrostaticfield having a voltage gradient of about 8,000 volts per inch is createdbetween the extended edge 25 and the grounded or earthed conductivesupport plate 29. Since the carpet 12 is processed over the underlyingbut earthed support plate 29, the high intensity field tends to passthrough the carpeting without significant reduction in its intensity.The several components comprising the polyurethane are admixed in mixinghead 32 and are fed to surface 28 of endless belt 13 at a rate of in therange of about 12 to about 25 cc per inch of width of the extended edge25. The endless belt is moving at a rate proportional to the rate ofmovement of the carpet l2 and has a width approximately equal to thewidth of the extended edge 25. It is important that belt 13 be displacedat a speed at which foaming of the polyurethane does not take place inthe nip between belt 13 and blade yet that the desired foam depth berealized on the carpet. Charged polyurethane particles are dispensedfrom the surface 28 of the endless belt 13 toward the carpeting. Movingthe carpeting at a rate of about 26 feet per minute past the extendededge results in a substantially uniform deposit of an adherent, expandedfoam of polyurethane on the carpeting having a substantially uniformthickness of about onesixteenth to about one-eighth of an inch dependingon the feed rate of the components to the belt 13 and the rate ofmovement of the carpeting.

After applying a substantially uniform deposit of polyurethane tocarpeting, the polyurethane is foamed and may be cured and aged by theapplication of a suitable elevated temperature for the required periodof time.

Polyurethane foams are the foam form of polyurethane resins.Polyurethane foam may be either rigid or flexible, hard and abrasive, orsoft and resilient, depending upon components, fillers and method offoaming. In providing a polyurethane foam a polyester such aspolyproylene glycol may be treated with a diisocyamate in the presenceof some water and a catalyst (amines, tin soaps, organic tin compounds)as well as fillers, dispersing and emulsifying agents, and othersubstances depending on the end product required. Simultaneously withthe polymer-forming reactions, the water reacts with the isocyanategroups to cause cross linking and curing, and also produces carbondioxide which causes foaming. In other methods, trifluoromethane orsimilar volatile material is incorporated to serve as blowing agent, andto reduce the thermal conductivity of the finished foam.

Usually, flexible polyurethane foams are based on polyoxypropylenediolsof 2,000 molecular weight and polyoxypropylene triols with molecularweight up to 4,000. The triols generally use glycerin as a startermaterial.

Rigid foams are based on polyethers made from compounds pounds such assorbitol, methyl glucoside, sucrose, and certain aromatic derivatives.

It is to be understood that the changes and modifications in theconcepts disclosed may be made by those skilled in the art withoutdeparting from the spirit and scope of the present invention. Suchmodifications are considered to be within the purview and scope of thepresent invention and the appended claims.

I claim:

1. An apparatus for providing charged particles of an organoplasticmaterial adapted to be projected toward a substrate comprising anelectrically insulative means comprising a traveling endless belt onwhich the organoplastic material is provided, a blade means including arelatively sharp wedge-shaped edge disposed within and transversely tosaid endless belt and associated therewith so as to configure said beltwith an attenuated edge, means including an extended edge at highpotential adapted to provide a high intensity electric field between theextended'edge and the substrate, the extended edge being relativelysharp and extending transversely across said belt and adjacent to saidattenutated edge, said extended edge being located so as to be incontact with the organoplastic material on the insulative means, theextended edge and the high intensity field cooperating to providecharged particles of the organoplastic material and means upstream ofthe attenuated edge for substantially uniformly distributing theorganoplastic material on the belt.

2. The apparatus of claim 1, wherein the means for substantiallyuniformly distributing the organoplastic material on insulative meansincludes a reciprocating mixing head and means for leveling theorganoplastic material on the insulative means.

3. The apparatus of claim 1, wherein the organoplastic material is aflexible polyurethane foam and the substrate is carpeting.

1. An apparatus for providing charged particles of an organoplasticmaterial adapted to be projected toward a substrate comprising anelectrically insulative means comprising a traveling endless belt onwhich the organoplastic material is provided, a blade means including arelatively sharp wedge-shaped edge disposed within and transversely tosaid endless belt and associated therewith so as to configure said beltwith an attenuated edge, means including an extended edge at highpotential adapted to provide a high intensity electric field between theextended edge and the substrate, the extended edge being relativelysharp and extending transversely across said belt and adjacent to saidattenutated edge, said extended edge being located so as to be incontact with the organoplastic material on the insulative means, theextended edge and the high intensity field cooperating to providecharged particles of the organoplastic material and means upstream ofthe attenuated edge for substantially uniformly distributing theorganoplastic material on the belt.
 2. The apparatus of claim 1, whereinthe means for substantially uniformly distributing the organoplasticmaterial on insulative means includes a reciprocating mixing head andmeans for leveling the organoplastic material on the insulative means.3. The apparatus of claim 1, wherein the organoplastic material is aflexible polyurethane foam and the substrate is carpeting.